Plastics frequently require the addition of additives. Such additives can be for example solid or liquid stabilisers, which in practice are used often not on their own, but together with further auxiliaries, such as lubricants. It is in this respect desirable to summarise relevant liquid and solid products.
Thus, from the German Auslegeschrift No. 1,544,697 is known the method of converting solid, particularly pulverulent, stabilisers, by fusing them together with lubricants, into suitable dust-free mixtures. The German Auslegeschrift No. 1,569,190 discloses a mixture, likewise formed in the melt, of a lubricant with solid stabilizers (component b). A similar mixture of solid, high-melting stabilizers with lubricants is described in the German Auslegeschrift No. 1,542,058.
Whereas therefore practicable suggestions have been made for combinations of solid stabilisers with lubricants, the combination of liquid stabilisers with solid lubricants has not hitherto been satisfactorily achieved. Liquid additives have thus so far been converted by absorption onto carrier substances, such as porous fillers or resins, into the solid form. This method has however the disadvantage that further additives find their way into the plastics material, a factor which is not always desirable, which frequently constitutes unnecessary filler material, and which can render necessary, for example, a renewed application for obtaining approval from the health authorities.
Various procedures for introducing requisite additives, including stabilizers, lubricants, pigments and fillers, into halogenated polymers such as poly(vinyl chloride), PVC, are described in U.S. Pat. Nos. 4,040,996 and 4,040,997. Among these is the concept of premixing a melted wax lubricant and stabilizer to form a homogeneous melt followed by cooling said melt. Unfortunately the resulting mixture is found to be an unsatisfactory semi-solid paste, difficult to handle in any practical way. Additionally the liquid stabilizer tends to migrate to the surface and to separate from the wax after only a few days storage. These patents point out that it has not been found possible to make a sufficiently complete and uniform mixture of additives and wax lubricants which can be handled in existing equipment and facilities to assure that each portion of the mixture chosen for mixing with a batch of PVC will have the same proportions of the different additives. This is a critical problem since some additives are used in the stabilized PVC in very low concentrations, such as 0.1 parts per hundred parts of resin.
Recognizing these inherent problems, U.S. Pat. No. 4,040,996 and 4,040,997 teach the use of aqueous emulsions of processing lubricants and stabilizers to coat the surface of selected pigments, fillers and mixtures thereof followed by evaporation of the water of the emulsion as a route to overcome the aforementioned difficulties with semi-solid paste mixtures of wax lubricants and PVC stabilizers.